/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.dx.dex;

/**
 * Constants that show up in and are otherwise related to {@code .dex} files,
 * and helper methods for same.
 */
public final class DexFormat {

	private DexFormat() {
	}

	/**
	 * API level to target in order to produce the most modern file format
	 */
	public static final int API_CURRENT = 14;

	/** API level to target in order to suppress extended opcode usage */
	public static final int API_NO_EXTENDED_OPCODES = 13;

	/**
	 * file name of the primary {@code .dex} file inside an application or
	 * library {@code .jar} file
	 */
	public static final String DEX_IN_JAR_NAME = "classes.dex";

	/** common prefix for all dex file "magic numbers" */
	public static final String MAGIC_PREFIX = "dex\n";

	/** common suffix for all dex file "magic numbers" */
	public static final String MAGIC_SUFFIX = "\0";

	/** dex file version number for the current format variant */
	public static final String VERSION_CURRENT = "036";

	/** dex file version number for API level 13 and earlier */
	public static final String VERSION_FOR_API_13 = "035";

	/**
	 * value used to indicate endianness of file contents
	 */
	public static final int ENDIAN_TAG = 0x12345678;

	/**
	 * Returns the API level corresponding to the given magic number, or
	 * {@code -1} if the given array is not a well-formed dex file magic number.
	 */
	public static int magicToApi(byte[] magic) {
		if (magic.length != 8) {
			return -1;
		}

		if ((magic[0] != 'd') || (magic[1] != 'e') || (magic[2] != 'x')
				|| (magic[3] != '\n') || (magic[7] != '\0')) {
			return -1;
		}

		String version = "" + ((char) magic[4]) + ((char) magic[5])
				+ ((char) magic[6]);

		if (version.equals(VERSION_CURRENT)) {
			return API_CURRENT;
		} else if (version.equals(VERSION_FOR_API_13)) {
			return 13;
		}

		return -1;
	}

	/**
	 * Returns the magic number corresponding to the given target API level.
	 */
	public static String apiToMagic(int targetApiLevel) {
		String version;

		if (targetApiLevel >= API_CURRENT) {
			version = VERSION_CURRENT;
		} else {
			version = VERSION_FOR_API_13;
		}

		return MAGIC_PREFIX + version + MAGIC_SUFFIX;
	}
}
